1. Field of the Invention
The present invention relates to methods and apparatus for joining the two ends of plastic optical fiber into a permanent splice having low transmission loss across the splice.
2. Related Art
Optical fibers are used to transmit information. If properly made, optical fibers permit the transmission of a wide band of frequencies with relatively little loss. Examples of use of optical fibers include intercity transmission of analog telephone and television information, digital data networks and high fidelity systems.
An optical fiber generally consists of a solid core, which may be transparent glass or plastic of a higher refractive index, and a cladding surrounding the core, the cladding, being a transparent material of a lower refractive index. The optical fiber is covered with a protective sheath which, in the case of plastic optical fiber, may be relatively thick compared to the optical fiber. The core generally is 0.5 to 2 mm i.d. (inner diameter) i.e., as thin as a human hair.
The joining (splicing) of the ends of glass or plastic optical fibers may be accomplished either by forming a permanent bond, for example, using a cemented joint or heat-welded joint, or by forming a connected bond using a mechanical connector. Such mechanical connectors are shown in U.S. Pat. Nos. 4,743,84; 4,778,243; 4,815,809; 4,890,896; 4,738,508 and 4,729,624.
In glass fibers the ends, after suitable treatment, may be spliced using an arc flame to weld the treated ends, see U.S. Pat. No. 4,957,343. In U.S. Pat. No. 4,790,617 the ends of two glass optical fibers are joined, within a tube, using an adhesive.
Plastic optical fibers, due to their relatively low cost, are preferable in some uses. Generally plastic optical fibers are formed of a transparent synthetic resin-based material, for example, polystyrene and resins, such as polymethylmethacrylate. Examples of such resins are given in U.S. Pat. No. 4,778,245.
In a physics study, many thousands of separate plastic optical fibers may be required to be individually connected to thousands of plastic plates or fibers having scintillator material which scintillates when bombarded with nuclear radiation, as in U.S. Pat. No. 4,788,436, incorporated by reference herein. However, such studies and the widespread use of plastic optical fibers are hindered due to the difficulty of forming splices which are low in transmission loss and which may be formed at relatively low cost. It would be expensive and time-consuming to make many thousands of splices using mechanical connectors or adhesive.